A computer system includes multiple devices that are necessary for its functioning. These devices must each be started or initialized when the system is powered on or restarted. Most computer systems include a system configuration manager program that handles the basic start up and initialization of the computer system.
In some computer systems the basic start up and initialization program or system configuration manager is referred to as the basic input-output system (BIOS). The computer system after power up or restart begins by executing the first instruction of the BIOS. The BIOS initializes the chipset, tests and initializes system memory, and tests and initializes peripheral device functionality. This process is collectively known as Power-on Self Test (POST). After system devices have been properly initialized the BIOS loads a boot-loader program. The boot-loader program is stored in the designated boot sector of a storage device such as a fixed disk. The boot-loader starts the operating system. The operating system then takes control of the computer system.
BIOS code is firmware that is stored in a flash memory device. The BIOS code uses configuration data to program user configurable settings during system POST. BIOS configuration data is stored in a nonvolatile memory that is composed of complementary metal oxide semiconductors (CMOS). CMOS is an energy efficient technology allowing it to be supported by a back up battery when a computer system is disconnected from its main power source. Non-volatile data used during POST includes real time clock (RTC) date and time data, drive configurations, system memory settings, operating system settings, serial and parallel port settings and other system settings.